The Utah Geological Survey says St. Louis-based Arch Coal is sacrificing 4 million tons of coal at the Dugout mine in Carbon County for safety.

A ton of coal sells for about $26.

Dugout still has plenty of other coal that can be mined. Arch plans to continue longwall mining there until 2015, following by a couple of years of retreat mining, said Michael Vanden Berg of the Utah Geological Survey.

Retreat mining  taking down pillars in a controlled collapse  can be risky. Federal regulators in a report issued Thursday said the operators of Crandall Canyon cut into load-bearing coal pillars, bringing down a large section of the mine.

The Aug. 6 collapse trapped six miners whose bodies haven't been recovered. Three others were killed during a rescue attempt.

Crandall Canyon was sealed off after last summer's twin disasters. In April, the same operator closed another central Utah mine, the 2,750-foot-deep Tower mine, because of "unusual stress conditions" on mine pillars there.